Quantum dot composite material, preparation method, and semiconductor device

ABSTRACT

A quantum dot (QD) composite material includes at least two structural units arranged sequentially along a radial direction. The at least two structural units include a type A1 structural unit and a type A2 structural unit. The type A1 QD structural unit has a gradient alloy composition structure with an energy level width increasing along the radial direction toward a surface, and the type A2 QD structural unit has a gradient alloy composition structure with the energy level width decreasing along the radial direction toward the surface. The two types of QD structural units are arranged alternately along the radial direction, and the energy levels in adjacent QD structural units having gradient alloy composition structures are continuous.

CROSS REFERENCE TO RELATED APPLICATIONS

The application claims priority to U.S. application Ser. No. 15/762,146, which is issued on Dec. 21, 2021 as U.S. Pat. No. 11,203,715; U.S. application Ser. No. 15/762,146 is a national phase of PCT application No. PCT/CN2017/080615, filed on Apr. 14, 2017, which claims priority to Chinese Patent Application No. CN201611255822X, filed on Dec. 30, 2016, the contents of all of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention generally relates to the field of quantum dot technology and, more particularly, relates to a quantum dot composite material, a preparation method, and a semiconductor device.

BACKGROUND

Quantum dot (QD) is a special material that is confined to a size in the order of nanometers in all three dimensions. The remarkable quantum confinement effect leads to many unique nano-properties of QDs, such as continuously-adjustable emission wavelength, narrow emission wavelength, wide absorption spectrum, high emission intensity, long fluorescence lifetime, excellent biocompatibility, etc. These unique properties make QDs have a wide range of applications in various fields including flat panel display, solid state lighting, photovoltaic solar energy, biomarker, etc. Particularly, in the field of flat panel display, benefiting from the nano-material properties and the optimization of QDs, QD light-emitting diode (QLED) devices, based on QD materials, have already demonstrated great potential in many aspects, including improving display quality, optimizing device performance, reducing manufacturing costs, etc. Although in recent years, the performance of QLED devices in all aspects has been continuously improved, there is still a considerable gap between the requirements of industrial applications and the basic device performance parameters, such as device efficiency, device stability, etc. This gap greatly hinders the development and application of the QD light-emitting display technologies. Moreover, the unique properties of QD materials relative to conventional materials have been increasingly valued not only in the field of QLED devices, but also in many other fields. For example, photoluminescent devices, solar cells, display devices, photoelectric detectors, biological probes, nonlinear optical devices, etc. have attracted more and more attention. In the following, QLED devices are provided as examples for further illustration.

Although QDs have been investigated and developed as a classical nanomaterial for over 30 years, the research time on utilizing the excellent light-emitting properties of QDs and using them as light-emitting materials in QLED devices and corresponding displays is still short. At present, most of the development and research of QLED devices is based on QD materials in existing classical structure systems. The corresponding standard for QD materials screening and optimization is mainly based on the consideration of the light-emitting properties of QDs, such as the light-emission peak width of the QDs, solution quantum yield, etc. The QDs are directly applied to the QLED structures to obtain the corresponding performance results of the devices.

However, because QLED device and the corresponding display may be a complex system of photoelectronic devices, the performance of the device may be affected by many factors. For example, in a case just considering a QD material as the material of a core light-emitting layer, the performance metrics of the QD that need to be weighed may have already been quite complicated.

First, in QLED devices, QDs are present in a QD light-emitting layer in a form of a solidified film. Therefore, each light-emission performance parameter of the QD materials originally obtained in solutions may be significantly different after being formed in the solidified films. For example, the light-emission peak wavelength in solidified films may have different degrees of red-shift (i.e., shifting to a longer wavelength), the light-emission peak may be broadened, or the quantum yield may be reduced to various degrees. That is, the excellent light-emitting properties of QD materials in solutions may not be fully transferred into the QD solidified films in QLED devices. Therefore, when designing and optimizing the structure and the synthesis formula for a QD material, it is necessary to take into account both the optimization of the light-emitting properties of the QD material and the maximization of the inheritance of the light-emitting performance in the solidified film of the QD material.

Moreover, in a QLED device, the QD material emits light through electro-induced excitation. That is, after holes and electrons are injected from the anode and the cathode of the QLED device, respectively, the holes and the electrons are transmitted through corresponding functional layers in the QLED device and recombined at the QD light-emitting layer, and through radiation transition, light may be emitted. It can be seen from the above process that the light-emitting properties, e.g. light-emission efficiency, of the QD may only affect the efficiency of the radiation transition in the above emission process. However, the overall light-emission efficiency of the QLED device may also be affected by various other factors during the emission process, such as the charge injection and transmission efficiency of the holes and the electrons in the QD material, the relative charge balance between the holes and the electrons in the QD material, the recombination region of the holes and the electrons in the QD material, etc. Therefore, when designing and optimizing the structure of a QD material, especially when designing and optimizing the fine core-shell nanostructure of a QD, special consideration may need to be focused on the electrical properties of the QD after forming a solidified film, such as the charge injection and conduction properties of the QD, the fine band structure of the QD, the exciton lifetime of the QD, etc.

Further, considering that QLED devices and the corresponding displays will be manufactured by solution processes, e.g. inkjet printing, which demonstrate significant advantages in production cost in the future, the material design and development of QDs may need to consider the processing properties of QD solutions, including the dispersible solubility of QD solutions or printing inks, the stability of colloids, the formability of the printed films, etc. In the meantime, the development of QD materials may also need to be in cooperation with other functional layers of the QLED devices as well as the overall preparation process and the requirements of the devices.

Therefore, the traditional QD structure design, which considers only the improvement of the light-emitting properties of the QDs, cannot meet the comprehensive requirements of QLED devices and the corresponding display technologies on optical properties, electrical properties, and processing properties of QD materials. It is necessary to optimize the fine core-shell structure, the composition, the energy level, and other related properties of the QD light-emitting materials based on the requirements of the QLED devices and the corresponding display technologies.

Because of the high surface atomic ratio of QD, atoms that do not form dangling bonds with surface ligands may exist as surface defect states. These surface defect states may cause transitions through a non-radiative manner so that the quantum yield of QD may be greatly reduced. To prevent the problem, a semiconductor shell containing a semiconductor material different from the material of the original QD may be grown on the outer surface of the original QD to form a QD with a core-shell structure. As such, the light-emitting properties of QD may be significantly improved and, in the meantime, the stability of the QD may also be improved.

The QD materials that can be applied to the development of high-performance QLED devices are mainly QDs that have core-shell structures. The compositions of the core and the shell are respectively fixed, and the boundary between the core and the shell is well defined. The examples of such QDs include QDs with a CdSe/ZnS core-shell structure (J. Phys. Chem., 1996, 100 (2), 468-471), QDs with a CdSe/CdS core-shell structure (J. Am. Chem. Soc. 1997, 119 (30), 7019-7029), QDs with a CdS/ZnS core-shell structure, QDs with a CdS/CdSe/CdS core-multilayer-shell structure (U.S. Pat. No. 7,919,012B2), QDs with a CdSe/CdS/ZnS core-multilayer-shell structure (J. Phy. Chem. B, 2004, 108 (49), 18826-18831), etc. In these QDs with core-shell structures, the compositions of the core and the shell are usually fixed, and are different from each other. In addition, the core-shell structure of these QDs is usually a binary compound system formed by a cation and an anion. In such a structure, because the core and the shell are grown independently and separately, the boundary between the core and the shell is well defined. That is, the core and the shell are distinguishable. As compared to the original single-composition QDs, the QDs with core-shell structures may improve the light-emission efficiency, the monodispersity, and the stability of the QDs.

Although the QDs with core-shell structures described above have partially improved the performance of QDs, the light-emitting performance of the QDs may still need to be improved because considerations for performance improvement are still based on how to improve light-emission efficiency of QD itself, no matter it is from the design strategy point of view, or from the optimization scheme point of view. Moreover, other special requirements of semiconductor devices on QD materials may also need to be taken into account in order to improve the performance of QDs.

Therefore, the existing technology of QD materials and corresponding semiconductor devices may still need to be improved and developed.

BRIEF SUMMARY OF THE INVENTION

In view of the above problems in the existing technology, the objective of the present invention is to provide a QD composite material, a preparation method, and a semiconductor device to improve the light-emitting performance of the existing QD materials, and thus solve the problem that the QD materials prepared by existing methods cannot meet the requirements of semiconductor devices.

The technical solution of the present invention is as follows.

-   -   synthesizing a first compound;     -   synthesizing a second compound on a surface of the first         compound, the second compound and the first compound having same         elements in different alloy compositions;     -   forming the QD composite material through a cation exchange         reaction between the first compound and the second compound, the         light-emission peak wavelength of the QD composite material         experiencing one or more of a blue-shift, a red-shift, and         no-shift.

In the method for preparing the QD composite material, the light-emission peak wavelength of the QD composite material experiences a continuous blue-shift.

In the method for preparing the QD composite material, the light-emission peak wavelength of the QD composite material experiences alternating blue-shifts and no-shifts.

In the method for preparing the QD composite material, the light-emission peak wavelength of the QD composite material experiences alternating blue-shifts and red-shifts.

In the method for preparing the QD composite material, the light-emission peak wavelength of the QD composite material experiences discontinuous blue-shifts.

In the method for preparing the QD composite material, the light-emission peak wavelength of the QD composite material experiences discontinuous red-shifts.

In the method for preparing the QD composite material, the light-emission peak wavelength of the QD composite material experiences a blue-shift and then remains unchanged.

In the method for preparing the QD composite material, the light-emission peak wavelength of the QD composite material experiences a continuous red-shift.

In the method for preparing the QD composite material, a cation precursor of the first compound and/or the second compound includes a zinc precursor. The zinc precursor includes at least one of dimethyl zinc, diethyl zinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide, zinc peroxide, zinc perchlorate, zinc sulfate, zinc oleate, and zinc stearate.

In the method for preparing the QD composite material, a cation precursor of the first compound and/or the second compound includes a cadmium precursor. The cadmium precursor includes at least one of dimethyl cadmium, diethyl cadmium, cadmium acetate, cadmium acetylacetonate, cadmium iodide, cadmium bromide, cadmium chloride, cadmium fluoride, cadmium carbonate, cadmium nitrate, cadmium oxide, cadmium perchlorate, cadmium phosphate, cadmium sulfate, cadmium oleate, and cadmium stearate.

In the method for preparing the QD composite material, an anion precursor of the first compound and/or the second compound includes a selenium precursor. The selenium precursor includes at least one of Se-TOP (selenium-trioctylphosphine), Se-TBP (selenium-tributylphosphine), Se-TPP (selenium-triphenylphosphine), Se-ODE (selenium-1-octadecene), Se-OA (selenium-oleic acid), Se-ODA (selenium-octadecylamine), Se-TOA (selenium-trioctylamine), Se-ODPA (selenium-octadecylphosphonic acid), and Se-OLA (selenium-oleylamine).

In the method for preparing the QD composite material, an anion precursor of the first compound and/or the second compound includes a sulfur precursor. The sulfur precursor includes at least one of S-TOP (sulfur-trioctylphosphine), S-TBP (sulfur-tributylphosphine), S-TPP (sulfur-triphenylphosphine), S-ODE (sulfur-1-octadecene), S-OA (sulfur-oleic acid), S-ODA (sulfur-octadecylamine), S-TOA (sulfur-trioctylamine), S-ODPA (sulfur-octadecylphosphonic acid), S-OLA (sulfur-oleylamine), and alkyl thiol.

In the method for preparing the QD composite material, an anion precursor of the first compound and/or the second compound includes a tellurium precursor. The tellurium precursor includes at least one of Te-TOP (tellurium-trioctylphosphine), Te-TBP (tellurium-tributylphosphine), Te-TPP (tellurium-triphenylphosphine), Te-ODE (tellurium-1-octadecene), Te-OA (tellurium-oleic acid), Te-ODA (tellurium-octadecylamine), Te-TOA (tellurium-trioctylamine), Te-ODPA (tellurium-octadecylphosphonic acid), and Te-OLA (tellurium-oleylamine).

In the method for preparing the QD composite material, the cation exchange reaction between the first compound and the second compound is performed under a heating condition.

In the method for preparing the QD composite material, a heating temperature is in a range of approximately 100° C. to 400° C.

In the method for preparing the QD composite material, a heating time is in a range of approximately 2 seconds to 24 hours.

In the method for preparing the QD composite material, a molar feed ratio of a cationic precursor to an anion precursor used for forming the first compound is in a range of approximately 100:1 to 1:50.

In the method for preparing the QD composite material, a molar feed ratio of a cationic precursor to an anion precursor used for forming the second compound is in a range of approximately 100:1 to 1:50.

A QD composite material, prepared by the method described above.

A semiconductor device including the QD composite material described above.

The semiconductor device is one of an electroluminescent device, a photoluminescent device, a solar cell, a display device, a photoelectric detector, a biological probe, and a nonlinear optical device.

Benefits: the QD composite material prepared by the method provided in the present invention may not only achieve high QD light-emission efficiency of the QD composite material, but also meet the comprehensive requirements of semiconductor devices and the corresponding display technologies on QD composite materials. Therefore, the disclosed QD composite material is a desired QD light-emitting material suitable for semiconductor devices and display technologies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of an energy-level structure of a quantum dot (QD) composite material having structure one consistent with some embodiments of the present invention.

FIG. 2 illustrates a schematic diagram of an energy-level structure of a QD composite material having structure two consistent with some embodiments of the present invention.

FIG. 3 illustrates a schematic diagram of an energy-level structure of a QD composite material having structure three consistent with some embodiments of the present invention.

FIG. 4 illustrates a schematic diagram of an energy-level structure of a QD composite material having structure four consistent with some embodiments of the present invention.

FIG. 5 illustrates a schematic diagram of an energy-level structure of a QD composite material having structure five consistent with some embodiments of the present invention.

FIG. 6 illustrates a schematic diagram of an energy-level structure of a QD composite material having structure six consistent with some embodiments of the present invention.

FIG. 7 illustrates a schematic diagram of an energy-level structure of a QD composite material having structure seven consistent with some embodiments of the present invention.

FIG. 8 illustrates a schematic diagram of the light-emission peak wavelength of a QD in Embodiment 10 of the present invention.

FIG. 9 illustrates a schematic diagram of the light-emission peak wavelength of a QD in Embodiment 11 of the present invention.

FIG. 10 illustrates a schematic diagram of the light-emission peak wavelength of a QD in Embodiment 12 of the present invention.

FIG. 11 illustrates a schematic structural view of a QD light-emitting diode in Embodiment 33 of the present invention.

FIG. 12 illustrates a schematic structural view of a QD light-emitting diode in Embodiment 34 of the present invention.

FIG. 13 illustrates a schematic structural view of a QD light-emitting diode in Embodiment 35 of the present invention.

FIG. 14 illustrates a schematic structural view of a QD light-emitting diode in Embodiment 36 of the present invention.

FIG. 15 illustrates a schematic structural view of a QD light-emitting diode in Embodiment 37 of the present invention.

FIG. 16 illustrates a schematic structural view of a QD light-emitting diode in Embodiment 38 of the present invention.

DETAILED DESCRIPTION

The present invention provides a quantum dot (QD) composite material, a preparation method, and a semiconductor device. To make the objectives, technical schemes and results more explicit, further description will be made in detail to illustrate the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not intended to limit the scope of the present invention.

The present invention provides a preparation method for a QD composite material. The preparation method may include the following steps:

-   -   synthesizing a first compound;     -   synthesizing a second compound on the surface of the first         compound, the first compound and the second compound having same         elements in different alloy compositions; and     -   forming a QD composite material through a cation exchange         reaction between the first compound and the second compound, the         light-emission peak wavelength of the QD material experiencing         one or more of a blue-shift, a red-shift, and no-shift.

The disclosed preparation method combines a successive ionic layer adsorption and reaction (STLAR) QD synthesis method together with a one-step QD synthesis method to form QDs. For example, the QD layer-by-layer growth method together with the one-step QD synthesis method may be used to form a composition-gradient transition shell. That is, two layers of thin-film compounds having same elements in different alloy compositions may be formed sequentially at a predetermined position; and through a cation exchange reaction between the two layers of compounds, a desired distribution of the alloy composition at the predetermined position may then be achieved. Repeating the process described above may continue to achieve the desired distribution of the alloy composition at various predetermined positions along the radial direction.

The first compound and the second compound can each be a binary compound or a compound containing more than two elements.

The QD composite material prepared by the disclosed method may include at least one QD structural unit arranged sequentially along a radial direction. The QD structural unit may have a gradient alloy composition structure with a changing energy level width along the radial direction or a homogeneous composition structure with a constant energy level width along the radial direction.

In other words, in the disclosed QD composite material, at any position from the center to the surface of each QD structural unit and along the radial direction, the QD structural unit may have an alloy composition structure within one or more monatomic layers.

Further, in present invention, the QD structural unit may include Group II and Group VI elements. The Group II elements may include, but are not limited to, Zn, Cd, Hg, Cn, etc. The Group VI elements may include, but are not limited to, O, S, Se, Te, Po, Lv, etc. For example, each QD structural unit may have an alloy composition structure of Cd_(x)Zn_(1-x)Se_(y)S_(1-y), where 0≤x≤1, 0≤y≤1, and x and y are not both 0 or 1 at the same time. It should be noted that the above only provides an example consistent with the embodiments of the present invention. For a QD structural unit having a gradient alloy composition structure, the composition at any position may be an alloy composition; for a QD structural unit having a homogeneous composition structure, the composition of the QD structural unit may be an alloy composition, or a non-alloy composition. In some embodiments, the composition of a QD structural unit is an alloy composition; that is, a homogeneous composition structure may be a homogeneous alloy composition structure. Further, in some embodiments, the homogeneous alloy composition may include Group II and Group IV elements. The following embodiments of the present invention are illustrated using a homogeneous alloy composition structure as an example. However, apparently, the embodiments are also applicable to a homogeneous composition structure of non-alloys

For illustrative purposes, a radial direction may refer to a direction from the center to the surface of a QD composite material. For example, when the QD composite material has a spherical structure or a sphere-like structure, a radial direction may be a direction along the radius of the spherical structure or the sphere-like structure. Similarly, a center (or an inner part) of the QD composite material may refer to the center of the physical structure of the QD composite material, and a surface (or an outer part) of the QD composite material may refer to the surface of the physical structure of the QD composite material.

In the following, various embodiments of the structures of the QD composite material of the present invention will be described in detail.

In one embodiment, the light-emitting wavelength of the QD composite material may experience a continuous blue-shift to achieve a desired gradient alloy composition distribution at the predetermined positions. When the light-emission peak wavelength experiences a blue-shift, the light-emission peak may move towards a shorter wavelength and, thus, the energy level width of the QD may become larger. As shown in FIG. 1 , along the radial direction of the QD, the energy level width of the QD structural unit may continuously become larger (i.e., experience a continuous blue-shift).

For example, as shown in FIG. 1 , the present invention provides a QD composite material having a funnel-shaped energy-level structure. The energy level width corresponding to the alloy composition of the QD structural units in the inner-part of the QD composite material may be smaller than the energy level width corresponding to the alloy composition of the QD structural units in the outer-part of the QD composite material. Specifically, the disclosed QD composite material may include at least one QD structural unit arranged sequentially along the radial direction. Each QD structural unit may have a gradient alloy composition structure with an energy level width increasing along the radial direction from the center to the surface. Moreover, the energy levels of adjacent gradient alloy composition structures of the QD structural units may be continuous. In the following, the structure of the QD composite material illustrated in FIG. 1 may be referred to as a specific structure 1. In the QD composite material illustrated in FIG. 1 , the energy level widths in adjacent QD structural units may have a continuous structure. That is, the energy level width may change continuously, rather than discontinuously/abruptly, between adjacent QD structural units. Accordingly, the alloy composition of the QD may also demonstrate continuity. In the following, the principle of continuous structure may be the same.

Further, in adjacent QD structural units along the radial direction, the energy level width in the QD structural unit closer to the center may be smaller than the energy level width in the QD structure unit farther away from the center. That is, in the disclosed QD composite material, the energy level width may gradually increase from the center to the surface, and thus form a funnel-shaped structure with a gradually increased opening. Specifically, the gradually increased opening may refer to that, in the energy-level structure shown in FIG. 1 , the energy level width may change continuously from the center of the QD composite material to the surface of the QD composite material. In the meantime, in the disclosed QD composite material, the energy level width may change continuously between adjacent QD structural units. That is, the alloy composition of the QD may also change continuously, which may be conducive to achieving high light-emission efficiency.

In other words, the specific structure 1 of the disclosed QD composite material may be a QD structure having a continuous gradient alloy composition from the center to the surface along the radial direction. That is, the composition of the QD structure may change continuously from the center to the surface along the radial direction. Accordingly, the distribution of the energy levels may also change continuously from the center to the surface along the radial direction. Therefore, the QD structure may demonstrate continuous changes in the composition and the distribution of the energy levels. Compared to QD materials with a well-defined boundary between the core and the shell, the disclosed QD composite material may not only be conducive to achieving higher light-emission efficiency, but also meet the comprehensive requirements of semiconductor devices and corresponding display technologies on QD composite materials. Therefore, the disclosed QD composite material is a desired QD light-emitting material suitable for semiconductor devices and display technologies.

Further, in the QD composite material shown in FIG. 1 , the alloy composition at point A (not shown) may be Cd_(x0) ^(A)Zn_(1-x0) ^(A)Se_(y0) ^(A)S_(1-y0) ^(A), and the alloy composition at point B (not shown) may be Cd_(x0) ^(B)Zn_(1-x0) ^(B)Se_(y0) ^(B)S_(1-y0) ^(B), where point A is closer to the center of the QD composite material than point B, and, the compositions at point A and point B satisfy: _(x0) ^(A)>_(x0) ^(B), _(y0) ^(A)>_(y0) ^(B). That is, for any two points in the QD composite material, e.g. point A and point B, when point A is closer to the center of the QD composite material than point B, _(x0) ^(A)>_(x0) ^(B), and _(y0) ^(A)>_(y0) ^(B). Therefore, when point A is closer to the center of the QD composite material than point B, the Cd concentration at point A may be larger than the Cd concentration at point B, the Zn concentration at point A may be smaller than the Cd concentration at point B, the Se concentration at point A may be larger than the Cd concentration at point B, and the S concentration at point A may be smaller than the Cd concentration at point B. As such, in the disclosed QD composite material, a gradient structure may be formed along the radial direction. In addition, along the radial direction from the center to the surface (i.e., along a direction away from the center of the QD composite material), the Cd concentration and the Se concentration may become lower, and the Zn concentration and the S concentration may become higher. According to the properties of these elements (i.e., Cd, Zn, Se, and S), the energy level width may increase.

In subsequently-provided various structures of the disclosed QD composite material, when a QD structural unit of the QD composite material has a gradient alloy composition structure with an energy level width increasing along the radial direction from the center to the surface, the alloy composition may be Cd_(x0)Zn_(1-x0)Se_(y0)S_(1-y0). For example, the alloy composition at point A may be Cd_(x0) ^(A)Zn_(1-x0) ^(A)Se_(y0) ^(A)S_(1-y0) ^(A), and the alloy composition at point B may be Cd_(x0) ^(B)Zn_(1-x0) ^(B)Se_(y0) ^(B)S_(1-y0) ^(B), where point A may be closer to the center of the QD composite material than point B, and the compositions at point A and point B satisfy: _(x0) ^(A)>_(x0) ^(B), _(y0) ^(A)>_(y0) ^(B). When a QD structural unit of the QD composite material has a gradient alloy composition structure with an energy level width decreasing along the radial direction from the center to the surface, the alloy composition of the QD structural unit may be Cd_(x0)Zn_(1-x0)Se_(y0)S_(1-y0). For example, the alloy composition at point C may be Cd_(x0) ^(C)Zn_(1-x0) ^(C)Se_(y0) ^(C)S_(1-y0) ^(C), and the alloy composition at point D may be Cd_(x0) ^(D)Zn_(1-x0) ^(D)Se_(y0) ^(D)S_(1-y0) ^(D), where point C is closer to the center of the QD composite material than point D, and the compositions at point C and point D satisfy: _(x0) ^(C)<_(x0) ^(D), _(y0) ^(C)<_(y0) ^(D). Moreover, when the QD structural unit of the QD composite material has a homogeneous composition structure (i.e., the energy level width is a constant along the radial direction from the center to the surface), the alloy composition may be Cd_(x0)Zn_(1-x0)Se_(y0)S_(1-y0). For example, the alloy composition at point E may be Cd_(x0) ^(E)Zn_(1-x0) ^(E)Se_(y0) ^(E)S_(1-y0) ^(E), and the alloy composition at point F may be Cd_(x0) ^(F)Zn_(1-x0) ^(F)Se_(y0) ^(F)S_(1-y0) ^(F), where point E is closer to the center of the QD composite material than point F, and the compositions at point E and point F satisfy: _(x0) ^(E)=_(x0) ^(F), _(y0) ^(E)=_(y0) ^(F).

In some embodiments, the light-emitting wavelength of the QD composite material may experience alternating blue-shifts and no-shifts. When the light-emission peak wavelength experiences a blue-shift, the light-emission peak may move towards a shorter wavelength and, thus, the energy level width of the QD may become larger. When the light-emission peak wavelength experiences no-shift, i.e. the light-emission peak wavelength is not shifted, the energy level width may remain unchanged. As shown in FIG. 2 , along the radial direction of the QD, the energy level width may become larger (i.e., blue-shift) in a first region, remain a same (i.e., no-shift) in a second region, and become larger (i.e., blue-shift) in a third region.

Further, as shown in FIG. 2 , the present invention also provides another QD composite material in which the energy level width corresponding to the inner-part alloy composition is smaller than or equal to the energy level width corresponding to the outer-part alloy composition, and at least one layer of QD structural units having a homogeneous composition structure exists between the center and the surface of the QD composite material. That is, the QD composite material may include at least three QD structural units arranged sequentially along the radial direction. Among the at least three QD structural units, each QD structural unit at a center of the QD composite material and each QD structural unit at a surface of the QD composite material may have a gradient alloy composition structure with an energy level width increasing along the radial direction from the center to the surface. Moreover, along the radial direction, the energy levels of adjacent gradient alloy composition structures of the QD structure units may be continuous. Further, a QD structural unit located between the QD structural units at the center and the QD structural units at the surface may have a homogeneous alloy composition structure. In the following, the structure of the QD composite material illustrated in FIG. 2 may be referred to as a specific structure 2.

For example, in the QD composite material shown in FIG. 2 , within a layer of QD structural units that have homogeneous alloy composition structures and are located between the QD structural units at the center and the QD structural units at the surface, the alloy composition at any position may be Cd_(x1)Zn_(1-x1)Se_(y1)S_(1-y1), where 0≤x1≤1, 0≤y1≤1, x1 and y1 are not both 0 or 1 at the same time, and each of x1 and y1 has a fixed value. For example, when the alloy composition at a position is Cd_(0.5)Zn_(0.5)Se_(0.5)S_(0.5), and the alloy composition at another point along the radial direction may also be Cd_(0.5)Zn_(0.5)Se_(0.5)S_(0.5). In another example, when the alloy composition at a position in a QD structural unit with a homogeneous alloy composition structure is Cd_(0.7)Zn_(0.3)S, and the alloy composition at another point in the QD structural unit may also be Cd_(0.7)Zn_(0.3)S. Similarly, when the alloy composition at a position in a QD structural unit with a homogeneous alloy composition structure is CdSe, and the alloy composition at another point in the QD structural unit may also be CdSe.

Further, in the QD composite material shown in FIG. 2 , each QD structural unit located at the center and each QD structural unit located at the surface may have a gradient alloy composition structure with an energy level width increasing along the radial direction from the center to the surface. In addition, the energy levels of adjacent gradient alloy composition structures of the QD structural units may be continuous. That is, in QD structural units having gradient alloy composition structures, the energy level width corresponding to the alloy composition at any position may be larger than the energy level width corresponding to the alloy composition at an adjacent position which is closer to the center of the QD structure. The alloy compositions in the QD structural units that have gradient alloy composition structures may be Cd_(x2)Zn_(1-x2)Se_(y2)S_(1-y2), where 0≤x2≤1, 0≤y2≤1, and x2 and y2 are not both 0 or 1 at the same time. For example, the alloy composition at a position is Cd_(0.5)Zn_(0.5)Se_(0.5)S_(0.5), and the alloy composition at another point may be Cd_(0.3)Zn_(0.7)Se_(0.4)S_(0.6).

In some embodiments, the light-emitting wavelength of the QD composite material may experience alternating blue-shifts and red-shifts. When the light-emission peak wavelength experiences a blue-shift, the light-emission peak may move towards a shorter wavelength and, thus, the energy level width of the QD may become larger. When the light-emission peak wavelength experiences a red-shift, the light-emission peak may move towards a longer wavelength and, thus, the energy level width of the QD may become smaller. As shown in FIG. 3 , along the radial direction of the QD, the energy level width may become larger (i.e., blue-shift) in a first region, become smaller (i.e., red-shift) in a second region, become larger (i.e., blue-shift) in a third region, become smaller (i.e., red-shift) in a fourth region, and become larger (i.e., blue-shift) in a fifth region.

For example, as shown in FIG. 3 , the present invention also provides another QD composite material having a fully-gradient alloy composition structure and containing quantum wells (QWs). That is, the disclosed QD composite material may include two types of QD structural units, i.e., type A1 and type A2, where type A1 QD structural units have a gradient alloy composition structure with the energy level width increasing along the radial direction towards the surface, and type A2 QD structural units have a gradient alloy composition structure with the energy level width decreasing along the radial direction towards the surface. Moreover, the two types of QD structural units may be arranged alternately along the radial direction, and the energy levels in adjacent QD structural units that have gradient alloy composition structures may be continuous. For example, the distribution of the QD structural units of the QD composite material may be A1, A2, A1, A2, A1 . . . , or A2, A1, A2, A1, A2 . . . . That is, the starting QD structural unit may be type A1 or type A2. In each type A1 QD structural unit, the energy level width may increase from the center to the surface, and in each type A2 QD structural unit, the energy level width may decrease from the center to the surface. Therefore, along the radial direction, both energy-level structures extend as wavy lines. In the following, the structure of the QD composite material illustrated in FIG. 3 may be referred to as specific structure 3.

In some embodiments, the light-emitting wavelength of the QD composite material may experience a discontinuous blue-shift. When the light-emission peak wavelength experiences a blue-shift, the light-emission peak may move towards a shorter wavelength and, thus, the energy level width of the QD may become larger. Moreover, when the light-emission peak wavelength experiences a red-shift, the light-emission peak may move towards a longer wavelength and, thus, the energy level width of the QD may become smaller; and when the light-emission peak wavelength experiences no-shift, i.e. the light-emission peak wavelength is not shifted, the energy level width may remain unchanged. The light-emission peak wavelength experiencing discontinuous blue-shifts represents that the energy level width between QD structural units may change abruptly/discontinuously, rather than continuously, as shown in FIG. 4 .

For example, as shown in FIG. 4 , the present invention also provides a QD composite material having an alloy composition structure and containing QWs with abrupt/discontinuous changes in the energy levels. For example, the QD structural units of the QD composite material may all have a gradient alloy composition structure with the energy level width increasing along the radial direction towards the surface, and the energy levels in adjacent QD structural units may be discontinuous. That is, the change in the energy level width between adjacent QD structural units may be discontinuous, i.e., the change may be characterized as a discontinuous/abrupt change in the energy level width. Accordingly, the alloy composition of the QD composite material may also change discontinuously/abruptly. Moreover, in the following, the principle of discontinuous structure may be the same, and the structure of the QD composite material illustrated in FIG. 4 may be referred to as a specific structure 4.

For example, the QD composition material shown in FIG. 4 may be formed by a plurality of QD structural units arranged in sequence through a discontinuous manner. The discontinuous manner may refer to having abrupt/discontinuous changes in the alloy compositions and the energy levels from a QD structural unit to an adjacent QD structural unit. The plurality of QD structural units may all have a gradient alloy composition structure with the energy level width increasing along the radial direction from the center to the surface. Moreover, in the QD composition material, the energy level width in QD structural units that are closer to the center may be smaller than the energy level width in QD structural units that are farther away from the center. That is, in the disclosed QD composition material, the energy level width may increase along the radial direction from the center to the surface, and thus form an intermittent funnel-shaped structure with an opening gradually increasing. Moreover, the disclosed QD composition material may not be limited to the embodiments provided above. For example, in other embodiments, the energy level width in the QD structural units that are closer to the center may be larger than the energy level width in the QD structural units that are farther away from the center. Accordingly, in the QD composition material, the energy level widths in adjacent QD structural units may have an overlapped range.

In some embodiments, the light-emitting wavelength of the QD composite material may experience discontinuous red-shifts. When the light-emission peak wavelength experiences a red-shift, the light-emission peak may move towards a longer wavelength and, thus, the energy level width of the QD may become smaller. Moreover, when the light-emission peak wavelength experiences a blue-shift, the light-emission peak may move towards a shorter wavelength and, thus, the energy level width of the QD may become larger; and when the light-emission peak wavelength experiences no-shift, i.e. the light-emission peak wavelength is not shifted, the energy level width may remain unchanged. The light-emission peak wavelength experiencing discontinuous red-shifts represents that the energy level width between QD structural units may change abruptly/discontinuously, rather than continuously, as shown in FIG. 5 .

For example, as shown in FIG. 5 , the present invention also provides another QD composite material having an alloy composition and containing QWs with abrupt/discontinuous changes in the energy levels. For example, the QD structural units of the QD composite material may all have a gradient alloy composition structure with the energy level width decreasing along the radial direction towards the surface, and the energy levels in adjacent QD structural units may be discontinuous. That is, the change in the energy level width between adjacent QD structural units may be discontinuous, i.e., the change may be characterized as a discontinuous/abrupt change in the energy level width. Therefore, the alloy composition of the QD composite material may also change discontinuously/abruptly. Moreover, in the following, the principle of discontinuous structure may be the same, and the structure of the QD composite material illustrated in FIG. 5 may be referred to as a specific structure 5.

For example, the QD composite material shown in FIG. 5 may be formed by a plurality of QD structural units arranged in sequence through a discontinuous manner. The plurality of QD structural units may all have a gradient alloy composition structure with the energy level width decreasing along the radial direction from the center to the surface. Moreover, in the QD composite material, the energy level width in QD structural units that are closer to the center may be larger than the energy level width in QD structural units that are farther away from the center. That is, in the disclosed QD composite material, the energy level width may become smaller along the radial direction from the center to the surface, and thus form an intermittent funnel-shaped structure with an opening gradually decreasing. Moreover, the disclosed QD composite material may not be limited to the embodiments provided above. For example, in other embodiments, the energy level width in QD structural units that are closer to the center may be smaller than the energy level width in QD structural units that are farther away from the center. Accordingly, in the QD composite material, the energy level widths in adjacent QD structural units may have an overlapped range.

In some embodiments, the light-emitting wavelength of the QD composite material may experience a blue-shift and then remain unchanged. When the light-emission peak wavelength experiences a blue-shift, the light-emission peak may move towards a shorter wavelength and, thus, the energy level width of the QD may become larger. When the light-emission peak wavelength remains unchanged, the light-emission peak may not be shifted and, thus, the energy level width may remain unchanged. As shown in FIG. 6 , along the radial direction of the QD, the energy level width may become larger (i.e., blue-shift) in a first region, and then remain unchanged (i.e., no-shift) in a second region.

For example, as shown in FIG. 6 , the present invention also provides a QD composite material, in which the energy level width of an alloy composition in a center region gradually increases from the center towards the surface, and a region close to the surface has a homogeneous alloy composition structure. For example, the QD composite material may include two types of QD structural units, i.e., type A3 and type A4, where type A3 QD structural units may have a gradient alloy composition structure with the energy level width increasing along the radial direction towards the surface, and type A4 QD structural units may have a homogeneous alloy composition structure. The inner part of the QD composite material may include one or more QD structural units having a gradient alloy composition structure. In addition, the energy levels in adjacent the QD structural units that have gradient alloy composition structures may be continuous. Moreover, the QD composite material may include one or more QD structural units having a homogeneous alloy composition structure in the region close to the surface. In the following, the structure of the QD composite material illustrated in FIG. 6 may be referred to as a specific structure 6.

For example, in the QD composite material shown in FIG. 6 , the distribution of the QD structural units of the QD composite material may be A3 . . . A3A4 . . . A4. That is, the inner part of the QD composite material may be formed by a plurality of type A3 QD structural units, and the outer part of the QD composite material may be formed by a plurality of type A4 QD structural units. Therefore, the number of the type A3 QD structural units and/or the number of the type A4 QD structural units may be larger than or equal to 1.

In some embodiments, the light-emitting wavelength of the QD composite material may experience a continuous red-shift. When the light-emission peak wavelength experiences a red-shift, the light-emission peak may move towards a longer wavelength and, thus, the energy level width of the QD may become smaller. When the light-emission peak wavelength experiences a blue-shift, the light-emission peak may move towards a shorter wavelength and, thus, the energy level width of the QD may become larger. When the light-emission peak wavelength is not changed, the energy level width may remain unchanged. The light-emission peak wavelength experiencing a red-shift may represent that the light-emission peak moves towards a longer wavelength, and thus along the radial direction of the QD, the energy level width of the QD structural unit may become smaller (i.e., red-shift).

In some embodiments, as shown in FIG. 7 , the present invention also provides another QD composite material, in which the energy level width of the alloy composition in a center region is a constant, and the energy level width of the alloy composition in an outer region gradually increases from the center to the surface. For example, the QD composite material may include two types of QD structural units, i.e., type A5 and type A6, where type A5 QD structural units may have a homogeneous alloy composition structure, and type A6 QD structural units may have a gradient alloy composition structure with the energy level width increasing along the radial direction towards the surface. The inner part of the QD composite material may include one or more than QD structural units having a homogeneous alloy composition structure. Moreover, the QD composite material may include one or more QD structural units having a gradient alloy composition structure in a region close to the surface. In addition, the energy levels in adjacent the QD structural units that have gradient alloy composition structures may be continuous. In the following, the structure of the QD composite material illustrated in FIG. 7 may be referred to as a specific structure 7.

For example, in the QD composite material shown in FIG. 7 , the distribution of the QD structural units of the QD composite material may be A5 . . . A5A6 . . . A6. That is, the inner part of the QD composite material may be formed by type A5 QD structural units, the outer part of the QD composite material may be formed by type A6 QD structural units, and the number of the type A5 QD structural units and/or the number of the type A6 QD structural units may be larger than or equal to 1.

Further, the QD structural units may each include 2-20 monatomic layers. In some embodiments, the QD structural units may each include 2-5 monatomic layers to ensure desired light-emitting quantum yield and high charge injection efficiency.

Further, the QD structural units may each include 1-10 unit-cell layers. For example, the QD structural units may each include 2-5 unit-cell layers. The unit-cell layer may be the smallest structural unit and, thus, the alloy composition of each unit-cell layer may be fixed. That is, within each unit-cell layer, the lattice parameters and the elements included may be the same. Each QD structural unit may be a closed unit-cell surface formed through the connection of the unit-cell layers, and the energy level width may have either a continuous change or a discontinuous/abrupt change between adjacent unit-cell layers.

The cation precursor of the first compound and/or the second compound may include a zinc precursor, including at least one of dimethyl zinc, diethyl zinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide, zinc peroxide, zinc perchlorate, zinc sulfate, zinc oleate, zinc stearate, etc.

The cation precursor of the first compound and/or the second compound may include a cadmium precursor, including at least one of dimethyl cadmium, diethyl cadmium, cadmium acetate, cadmium acetylacetonate, cadmium iodide, cadmium bromide, cadmium chloride, cadmium fluoride, cadmium carbonate, cadmium nitrate, cadmium oxide, cadmium perchlorate, cadmium phosphate, cadmium sulfate, cadmium oleate, and cadmium stearate, etc.

The anion precursor of the first compound and/or the second compound may include a selenium precursor, such as compounds formed by Se and any appropriate organic material. For example, the selenium precursor may include at least one of Se-TOP (selenium-trioctylphosphine), Se-TBP (selenium-tributylphosphine), Se-TPP (selenium-triphenylphosphine), Se-ODE (selenium-1-octadecene), Se-OA (selenium-oleic acid), Se-ODA (selenium-octadecylamine), Se-TOA (selenium-trioctylamine), Se-ODPA (selenium-octadecylphosphonic acid), Se-OLA (selenium-oleylamine), etc.

The anion precursor of the first compound and/or the second compound may include a sulfur precursor, such as compounds formed by S and any appropriate organic material. For example, the sulfur precursor may include at least one of S-TOP (sulfur-trioctylphosphine), S-TBP (sulfur-tributylphosphine), S-TPP (sulfur-triphenylphosphine), S-ODE (sulfur-1-octadecene), S-OA (sulfur-oleic acid), S-ODA (sulfur-octadecylamine), S-TOA (sulfur-trioctylamine), S-ODPA (sulfur-octadecylphosphonic acid), S-OLA (sulfur-oleylamine), etc. Alternatively, the sulfur precursor may be alkyl thiol, including at least one of hexanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, mercaptopropylsilane, etc.

The anion precursor of the first compound and/or the second compound may also include a tellurium precursor, including at least one of Te-TOP (tellurium-trioctylphosphine), Te-TBP (tellurium-tributylphosphine), Te-TPP (tellurium-triphenylphosphine), Te-ODE (tellurium-1-octadecene), Te-OA (tellurium-oleic acid), Te-ODA (tellurium-octadecylamine), Te-TOA (tellurium-trioctylamine), Te-ODPA (tellurium-octadecylphosphonic acid), Te-OLA (tellurium-oleylamine), etc.

Based on the QD material to be formed, one or more compounds may be selected for the cation precursor and the anion precursor. For example, to synthesize QD materials with an alloy composition of Cd_(x)Zn_(1-x)Se_(y)S_(1-y), a cadmium precursor, a zinc precursor, a selenium precursor, and a sulfur precursor may be required; to synthesize QD materials with an alloy composition of Cd_(x)Zn_(1-x)S, a cadmium precursor, a zinc precursor, and a sulfur precursor may be required; to synthesize QD materials with an alloy composition of Cd_(x)Zn_(1-x)Se, a cadmium precursor, a zinc precursor, and a selenium precursor may be required.

In the disclosed preparation method, the condition for the cation exchange reaction may be a heating condition. For example, the heating temperature may be in a range of approximately 100° C. to 400° C. In some embodiments, the heating temperature may be in a range of approximately 150° C. to 380° C. A heating time may be in a range of approximately 2 seconds to 24 hours. In some embodiments, the heating time may be in a range of approximately 5 minutes to 4 hours.

When the heating temperature is higher, the reaction rate of the cation exchange reaction may be larger, and the thickness range and the degree of the cation exchange may also become larger. However, the thickness range and the degree of the cation exchange may be gradually saturated. Similarly, when the heating time is longer, the thickness range and the degree of the cation exchange may become larger; however, the thickness range and the degree of the cation exchange may also be gradually saturated. The thickness range and the degree of exchange reaction may directly determine the distribution of the gradient alloy composition. In the meantime, the distribution of the gradient alloy composition formed through the cation exchange reaction may also be determined by the thickness of the binary or the multi-element-containing QD composite material that are formed separately.

When forming each layer of compound, the cation precursor and the anion precursor may have a molar feed ratio in a range of approximately 100:1 to 1:50. For example, when forming the first layer of compound, the molar feed ratio of the cation precursor and the anion precursor may be in a range of approximately 100:1 to 1:50; when forming a second layer of compound, the molar feed ratio of the cation precursor and the anion precursor may be in a range of approximately 100:1 to 1:50. In some embodiments, the molar feed ratio of the cation precursor and the anion precursor may be in a range of approximately 20:1 to 1:10. Having a molar feed ratio of the cation precursor and the anion precursor in a range of approximately 20:1 to 1:10 may ensure the reaction rate within a range that can be easily controlled.

The present invention also provides a QD composite material. The QD composite material may be prepared by the method described above.

For a QD composite material prepared by the disclosed preparation method, the light-emission peak wavelength may be in a range of approximately 400 nm to 700 nm. In some embodiments, the light-emission peak wavelength may be in a range of approximately 430 nm to 660 nm to achieve a light-emitting quantum yield larger than 30%.

For a QD composite material prepared by the disclosed preparation method, the light-emitting quantum yield may be in a range of approximately 1% to 100%. In some embodiments, to ensure that the QDs have desired applicability, the light-emitting quantum yield may be in a range of approximately 30% to 100%.

Further, in the present invention, the full width at half maximum (FWHM) of the light-emission peak of the QD composite material may be in a range of approximately 12 nm to 80 nm.

The present invention also provides a semiconductor device including a QD composite material consistent with the above description.

The semiconductor device may be one of an electroluminescent device, a photoluminescent device, a solar cell, a display device, a photoelectric detector, a biological probe, and a nonlinear optical device.

Taking an electroluminescent device as an example, a QD composite material provided in the present invention may be used as the material of a light-emitting layer in a QD electroluminescent device. The QD electroluminescent device may be able to achieve: 1) highly efficient charge injection; 2) high luminous brightness; 3) low driving voltage; 4) high device efficiency, and other desired device performance. At the same time, the disclosed QD composite material may also be easily controlled and may have a variety of energy-level structures. Therefore, the disclosed material may be able to fully meet and cooperate with the energy-level structures of other functional layers of the device to achieve overall matching of the energy-level structures in the device and, thus, may help achieve a highly-efficient semiconductor device.

The photoluminescent device may refer to a device that relies on irradiation of an external light source to obtain energy, generate excitation, and emit light. Ultraviolet radiation, visible light and infrared radiation can all lead to photoluminescence, including phosphorescence and fluorescence. The disclosed QD composite material may be used as a light-emitting material of a photoluminescent device.

The solar cell is also called a photovoltaic device. The disclosed QD composite material may be used as a light-absorption material of a solar cell to effectively improve various performance parameters of the photovoltaic device.

The display device may refer to a backlight module or a display panel adopting the backlight module. The display panel may be used in various products, including display screens, tablets, cell phones, notebook computers, flat-screen TVs, wearable display devices, and other products containing display panels in different sizes.

The photodetector may refer to a device that is able to convert optical signals into electrical signals. The principle of the photodetector is based on changes in the conductivity of a material upon irradiation. When a QD composite material is used in a photodetector, the photodetector may demonstrate the following advantages: sensitivity to normally incident light, high photoconductivity, high contrast detection rate, continuously-adjustable detection wavelength, and capability for low-temperature manufacturing. During the operation of a photodetector using the disclosed QD composite material, the photogenerated electron-hole pairs created after the photosensitive layer of the QD absorbs photons can be separated by a built-in electric field. As such, the driving voltage of the photodetector that uses the disclosed QD composite material may be lower. For example, the photodetector may be able to operate with a low applied bias voltage, or even with a zero bias voltage, and may be easily controlled.

The biological probe may refer to a device used for modifying certain type of materials to provide such materials with a marking function. For example, a QD composite material provided in the present invention may be coated to form a fluorescent probe used in the field of cell imaging or material detection. Compared to the traditional organic fluorescent dye probe, the biological probe prepared by using the disclosed QD composite material may have advanced characteristics such as high fluorescence intensity, desired chemical stability, and strong resistance to light bleaching. Therefore, the biological probe prepared by using the disclosed QD composite material may have a wide range of applications.

The nonlinear optical device may belong to the field of optical laser technology, and may have a wide range of applications. The applications of the nonlinear optical device may include the following examples. The nonlinear optical device may be used for electro-optic switching and laser modulation, may be used for laser frequency conversion and laser frequency tuning, may be used to process optical information and improve image quality and beam quality, may be used as a nonlinear etalon or a bistable device, and may be used for studying the highly-excited states and the high-resolution spectra of matter as well as the internal energy and excitation transfer process and other relaxation processes.

Embodiment 1: Preparation of a CdZnSeS/CdZnSeS-based QD

First, a cationic cadmium precursor, a cationic zinc precursor, an anionic selenium precursor, and an anionic sulfur precursor may be injected into a reaction system to form a Cd_(y)Zn_(1-y)Se_(b)S_(1-b) layer, where 0≤y≤1, 0≤b≤1. Further, the cationic cadmium precursor, the cationic zinc precursor, the anionic selenium precursor, and the anionic sulfur precursor may be continuously injected into the reaction system to form a Cd_(z)Zn_(1-z)Se_(c)S_(1-c) layer on the surface of the Cd_(y)Zn_(1-y)Se_(b)S_(1-b) layer, where 0≤z≤1, 0≤c≤1, and z is not equal to y. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, exchanges between Cd ions and Zn ions may take place in the inner layer and the outer layer of the QD composite material (i.e., the two layers of compounds). Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution with varying Cd and Zn concentrations, i.e., Cd_(x)Zn_(1-x)Se_(a)S_(1-a), where 0≤x≤1, 0≤a≤1, may be formed at the interface between the Cd_(y)Zn_(1-y)Se_(b)S_(1-b) layer and the Cd_(z)Zn_(1-z)Se_(c)S_(1-e) layer.

Embodiment 2: Preparation of a CdZnS/CdZnS-Based QD

First, a cationic cadmium precursor, a cationic zinc precursor, and an anionic sulfur precursor may be injected into a reaction system to form a Cd_(y)Zn_(1-y)S layer, where 0≤y≤1. Further, the cationic cadmium precursor, the cationic zinc precursor, and the anionic sulfur precursor may be continuously injected into the reaction system to form a Cd_(z)Zn_(1-z)S layer on the surface of the Cd_(y)Zn_(1-y)S layer, where 0≤z≤1, and z is not equal to y. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, exchanges between Cd ions and Zn ions may take place in the inner layer and the outer layer of the QD composite material (i.e., the two layers of compounds). Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution with varying Cd and Zn concentrations, i.e., Cd_(x)Zn_(1-x)S, where 0≤x≤1, may be formed at the interface between the Cd_(y)Zn_(1-y)S layer and the Cd_(z)Zn_(1-z)S layer.

Embodiment 3: Preparation of a CdZnSe/CdZnSe-Based QD

First, a cationic cadmium precursor, a cationic zinc precursor, and an anionic selenium precursor may be injected into a reaction system to form a Cd_(y)Zn_(1-y)Se layer, where 0≤y≤1. Further, the cationic cadmium precursor, the cationic zinc precursor, and the anionic selenium precursor may be continuously injected into the reaction system to form a Cd_(z)Zn_(1-z)Se layer on the surface of the Cd_(y)Zn_(1-y)Se layer, where 0≤z≤1, and z is not equal to y. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, exchanges between Cd ions and Zn ions may take place in the inner layer and the outer layer of the QD composite material (i.e., the two layers of compounds). Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution with varying Cd and Zn concentrations, i.e., Cd_(x)Zn_(1-x)Se, where 0≤x≤1, may be formed at the interface between the Cd_(y)Zn_(1-y)Se layer and the Cd_(z)Zn_(1-z)Se layer.

Embodiment 4: Preparation of a CdS/ZnS-Based QD

First, a cationic cadmium precursor and an anionic sulfur precursor may be injected into a reaction system to form a CdS layer. Further, a cationic zinc precursor together with the anionic sulfur precursor may be injected into the reaction system to form a ZnS layer on the surface of the CdS layer. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, the Zn cations in the outer layer may be gradually migrate to the inner layer and, thus, may exchange with the Cd ions in the inner layer. Similarly, the Cd ions in the inner layer may be gradually migrate to the out layer and, thus, may exchange with the Zn ions in the outer layer. Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution, with the Cd concentration gradually decreasing while the Zn concentration gradually increasing along the radial direction from the inner layer to the outer layer, i.e., Cd_(x)Zn_(1-x)S, where 0≤x≤1, may be formed near the interface between the CdS layer and the ZnS layer. In addition, the value of x may change monotonically from 1 to 0 along the direction from the inner layer to the outer layer (i.e., the radial direction).

Embodiment 5: Preparation of a CdSe/ZnSe-Based QD

First, a cationic cadmium precursor and an anionic selenium precursor may be injected into a reaction system to form a CdS layer. Further, a cationic zinc precursor together with the anionic selenium precursor may be injected into the reaction system to form a ZnSe layer on the surface of the CdSe layer. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, the Zn cations in the outer layer may be gradually migrate to the inner layer and, thus, may exchange with the Cd ions in the inner layer. Similarly, the Cd ions in the inner layer may be gradually migrate to the out layer and, thus, may exchange with the Zn ions in the outer layer. Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution, with the Cd concentration gradually decreasing while the Zn concentration gradually increasing along the radial direction from the inner layer to the outer layer, i.e., Cd_(x)Zn_(1-x)Se, where 0≤x≤1, may be formed near the interface between the CdSe layer and the ZnSe layer. In addition, the value of x may decrease monotonically from 1 to 0 along the direction (i.e., the radial direction) from the inner layer to the outer layer.

Embodiment 6: Preparation of a CdSeS/ZnSeS-Based QD

First, a cationic cadmium precursor, an anionic selenium precursor, and an anionic sulfur precursor may be injected into a reaction system to form a CdSe_(b)S_(1-b) layer, where 0≤b≤1. Further, a cationic zinc precursor together with the anionic selenium precursor and the anionic sulfur precursor may be continuously injected into the reaction system to form a ZnSe_(c)S_(1-c) layer on the surface of the CdSe_(b)S_(1-b) layer, where 0≤c≤1. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, the Zn cations in the outer layer may be gradually migrate to the inner layer and, thus, may exchange with the Cd ions in the inner layer. Similarly, the Cd ions in the inner layer may be gradually migrate to the out layer and, thus, may exchange with the Zn ions in the outer layer. Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution, with the Cd concentration gradually decreasing while the Zn concentration gradually increasing along the radial direction from the inner layer to the outer layer, i.e., Cd_(x)Zn_(1-x)Se_(a)S_(1-a), where 0≤x≤1 and 0≤a≤1, may be formed near the interface between the CdSe_(b)S_(1-b) layer and the ZnSe_(c)S_(1-c) layer. In addition, the value of x may decrease monotonically from 1 to 0 along the direction (i.e., the radial direction) from the inner layer to the outer layer.

Embodiment 7: Preparation of a ZnS/CdS-Based QD

First, a cationic zinc precursor and an anionic sulfur precursor may be injected into a reaction system to form a ZnS layer. Further, a cationic cadmium precursor together with the anionic sulfur precursor may be continuously injected into the reaction system to form a CdS layer on the surface of the ZnS layer. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, the Cd cations in the outer layer may be gradually migrate to the inner layer and, thus, may exchange with the Zn ions in the inner layer. Similarly, the Zn ions in the inner layer may be gradually migrate to the out layer and, thus, may exchange with the Cd ions in the outer layer. Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution, with the Zn concentration gradually decreasing while the Cd concentration gradually increasing along the radial direction from the inner layer to the outer layer, i.e., Cd_(x)Zn_(1-x)S, where 0≤x≤1, may be formed near the interface between the ZnS layer and the CdS layer. In addition, the value of x may increase monotonically from 0 to 1 along the direction (i.e., the radial direction) from the inner layer to the outer layer.

Embodiment 8: Preparation of a ZnSe/CdSe-Based QD

First, a cationic zinc precursor and an anionic selenium precursor may be injected into a reaction system to form a ZnSe layer. Further, a cationic cadmium precursor together with the anionic selenium precursor may be continuously injected into the reaction system to form a CdSe layer on the surface of the ZnSe layer. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, the Cd cations in the outer layer may be gradually migrate to the inner layer and, thus, may exchange with the Zn ions in the inner layer. Similarly, the Zn ions in the inner layer may be gradually migrate to the out layer and, thus, may exchange with the Cd ions in the outer layer. Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution, with the Zn concentration gradually decreasing while the Cd concentration gradually increasing along the radial direction from the inner layer to the outer layer, i.e., Cd_(x)Zn_(1-x)Se, where 0≤x≤1, may be formed near the interface between the ZnSe layer and the CdSe layer. In addition, the value of x may increase monotonically from 0 to 1 along the direction (i.e., the radial direction) from the inner layer to the outer layer.

Embodiment 9: Preparation of a ZnSeS/CdSeS-Based QD

First, a cationic zinc precursor, an anionic selenium precursor, and an anionic sulfur precursor may be injected into a reaction system to form a ZnSe_(b)S_(1-b) layer, where 0≤b≤1. Further, a cationic cadmium precursor together with the anionic selenium precursor and the anionic sulfur precursor may be continuously injected into the reaction system to form a ZnSe_(c)S_(1-c) layer on the surface of the ZnSe_(b)S_(1-b) layer, where 0≤c≤1. Under certain reaction conditions including an appropriate heating temperature and an appropriate heating time, the Cd cations in the outer layer may be gradually migrate to the inner layer and, thus, may exchange with the Zn ions in the inner layer. Similarly, the Zn ions in the inner layer may be gradually migrate to the out layer and, thus, may exchange with the Cd ions in the outer layer. Moreover, the migration distance of the cations is limited, and the migration probability decreases as the migration distance increases. Therefore, a gradient alloy composition distribution, with the Zn concentration gradually decreasing while the Cd concentration gradually increasing along the radial direction from the inner layer to the outer layer, i.e., Cd_(x)Zn_(1-x)Se_(a)S_(1-a), where 0≤x≤1 and 0≤a≤1, may be formed near the interface between the ZnSe_(b)S_(1-b) layer and the ZnSe_(c)S_(1-c) layer. In addition, the value of x may increase monotonically from 0 to 1 along the direction (i.e., the radial direction) from the inner layer to the outer layer.

Embodiment 10: Preparation of a Blue QD Cd_(x)Zn_(1-x)S with the Specific Structure 1

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system, and Cd_(x)Zn_(1-x)S may quickly nucleate. After 10 minutes of reaction, 3 mL of the sulfur-trioctylphosphine precursor and 6 mL of the cadmium oleate precursor may be added dropwise to the reaction system with injection rates of 3 mL/h and 10 mL/h, respectively. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol and precipitated, and then purified by centrifugation. As such, a blue QD (Cd_(x)Zn_(1-x)S) having the specific structure 1 may be obtained, and the blue QD may have a funnel-shaped energy-level structure with a gradually increased opening. As shown in FIG. 8 , the light-emission peak wavelength of the blue QD may be 453 nm, and the absorbance of the blue QD may gradually decrease with increasing wavelength

Embodiment 11: Preparation of a Green QD Cd_(x)Zn_(1-x)Se_(y)S_(1-y)/Cd_(z)Zn_(1-z)S with the Specific Structure 1

Preparation of a cadmium oleate and zinc oleate precursor: 0.4 mmol of cadmium oxide (CdO), 8 mmol of zinc acetate [Zn(acet)₂], and 10 mL of oleic acid may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder and 4 mmol of sulfur powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

2 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be rapidly injected into the reaction system, and Cd_(x)Zn_(1-x)Se_(y)S_(1-y) may quickly nucleate. After 10 minutes of reaction, 2 mL of the sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 8 mL/h until the precursor is completely injected. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a green QD (Cd_(x)Zn_(1-x)Se_(y)S_(1-y)/Cd_(z)Zn_(1-z)S) having the specific structure 1 may be obtained, and the green QD may have a funnel-shaped energy-level structure with a gradually increased opening. As shown in FIG. 9 , the light-emission peak wavelength of the green QD may be 542 nm, and the absorbance of the green QD may gradually decrease with increasing wavelength.

Embodiment 12: Preparation of a Red QD Cd_(x)Zn_(1-x)Se_(y)S_(1-y)/Cd_(z)Zn_(1-z)S with the Specific Structure 1

Preparation of a cadmium oleate and zinc oleate precursor: 0.8 mmol of cadmium oxide (CdO), 12 mmol of zinc acetate [Zn(acet)₂], and 14 mL of oleic acid may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

0.2 mmol of selenium powder and 0.6 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine precursor may be rapidly injected into the reaction system, and Cd_(x)Zn_(1-x)Se may quickly nucleate. After 10 minutes of reaction, 2 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 4 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a red QD (Cd_(x)Zn_(1-x)Se_(y)S_(1-y)/Cd_(z)Zn_(1-z)S) having the specific structure 1 may be obtained, and the red fluorescent QD may have a funnel-shaped energy-level structure with a gradually increased opening. As shown in FIG. 10 , the light-emission peak wavelength of the red QD may be 631 nm, and the absorbance of the red QD may gradually decrease with increasing wavelength.

Embodiment 13: Influence of the Injection Rate of the Cadmium Oleate Precursor on the Preparation of a Blue QD with the Specific Structure 1

Based on the exemplary method described in Embodiment 10, the preparation method for the blue QD may further adjust the injection rate of the cadmium oleate precursor to control the slope of the composition gradient of the QD and, thus, change the variation of the funnel-shaped energy-level structure to further realize the control of the emission wavelength of the QD.

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system, and Cd_(x)Zn_(1-x)S may quickly nucleate. After 10 minutes of reaction, 3 mL of the sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 3 mL/h, and in the meantime, the cadmium oleate precursor may also be added dropwise to the reaction system at different rates. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol and precipitated, and then purified by centrifugation to obtain a blue QD (Cd_(x)Zn_(1-x)S/Cd_(y)Zn_(1-y)S) having a funnel-shaped energy-level structure with a gradually increased opening.

A list of the adjusted emission wavelengths of various QDs, prepared based on a same QD center (an alloy QD with a light-emission peak wavelength of 447 nm) and different injection rates of the cadmium oleate precursor, is as follows:

Injection rate of the cadmium oleate precursor Emission wavelength (mmol/h) (nm) 0.5 449 0.75 451 1 453 1.25 455 1.5 456

Embodiment 14: Influence of the Injection Volume of the Cadmium Oleate Precursor on the Preparation of a Blue QD with the Specific Structure 1

Based on the methods described in Embodiment 10 and Embodiment 13, the preparation method for the blue QD may further adjust the injection volume of the cadmium oleate precursor to control the range of gradient change of the composition of the QD and, thus, change the funnel-shaped energy-level structure to further realize the control of the emission wavelength of the QD. A list of the adjusted emission wavelengths of various QDs, prepared based on a same QD center (an alloy QD with a light-emission peak wavelength of 447 nm) and different injection volumes of the cadmium oleate precursor (under a same injection rate of 1 mmol/h), is as follows:

Injection volume of the cadmium oleate precursor Emission wavelength (mmol) (nm) 0.4 449 0.5 451 0.6 453 0.8 454 1.0 455

Embodiment 15: Preparation of a Blue QD with the Specific Structure 2

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)S. After 10 minutes of reaction, the temperature of the reaction system may be reduced to 280° C. Further, 2 mL of the sulfur-trioctylphosphine precursor and 6 mL of the cadmium oleate precursor may be simultaneously added dropwise to the reaction system with injection rates of 3 mL/h and 10 mL/h, respectively. 40 minutes after the injection of the sulfur-trioctylphosphine precursor and the cadmium oleate precursor, the temperature of the reaction system may be increased to 310° C., and 1 mL of the sulfur-trioctylphosphine precursor may then be added to the reaction system with an injection rate of 3 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol and precipitated, and then purified by centrifugation. As such, a blue QD having a QW energy-level structure may be obtained.

Embodiment 16: Preparation of a Green QD with the Specific Structure 2

Preparation of a cadmium oleate and zinc oleate precursor: 0.4 mmol of cadmium oxide (CdO), 8 mmol of zinc acetate [Zn(acet)₂], 10 mL of oleic acid, and 20 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder and 4 mmol of sulfur powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

2 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se_(y)S_(1-y). After 10 minutes of reaction, the temperature of the reaction system may be reduced to 280° C. Further, 1.2 mL of the sulfur-trioctylphosphine precursor and 6 mL of the cadmium oleate precursor may be simultaneously added dropwise to the reaction system with injection rates of 2 mL/h and 10 mL/h, respectively until the precursors are completely injected. Further, the temperature of the reaction system may be increased to 310° C., and 0.8 mL of the sulfur-trioctylphosphine precursor may then be added to the reaction system with an injection rate of 2 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a green QD having a QW energy-level structure may be obtained.

Embodiment 17: Preparation of a Red QD with the Specific Structure 2

Preparation of a cadmium oleate and zinc oleate precursor: 0.8 mmol of cadmium oxide (CdO), 12 mmol of zinc acetate [Zn(acet)₂], 14 mL of oleic acid, and 20 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

0.2 mmol of selenium powder and 0.6 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

0.3 mmol of cadmium oxide (CdO), 0.3 mL of oleic acid, and 2.7 mL of 1-octadecene may be placed in a 50 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se. After 10 minutes of reaction, the temperature of the reaction system may be reduced to 280° C. Further, 1 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor and 3 mL of the cadmium oleate precursor may be added dropwise to the reaction system with injection rates of 2 mL/h and 6 mL/h, respectively. Further, the temperature of the reaction system may be increased to 310° C., and 1 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may then be added to the reaction system with an injection rate of 4 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a red QD having a QW energy-level structure may be obtained.

Embodiment 18: Preparation of a Blue QD with the Specific Structure 3

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.2 mmol of selenium powder may be dissolved in 1 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system to form quickly nucleated Cd_(x)Zn_(1-x)S. After 10 minutes of reaction, the cadmium oleate precursor and the sulfur-trioctylphosphine precursor may be continuously injected into the reaction system with injection rates of 0.6 mmol/h and 4 mmol/h, respectively for 20 minutes. Further, the cadmium oleate precursor, the sulfur-trioctylphosphine precursor, and the selenium-trioctylphosphine precursor may then be continuously injected into the reaction system with injection rates of 0.4 mmol/h, 0.6 mmol/h, and 0.2 mmol/h, respectively for 1 hour. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol and precipitated, and then purified by centrifugation. As such, a blue QD (CdZnS/CdZnS/CdZnSeS₃) having a QW energy-level structure may be obtained.

Embodiment 19: Preparation of a Green QD with the Specific Structure 3

Preparation of a cadmium oleate and zinc oleate precursor: 0.4 mmol of cadmium oxide (CdO), 6 mmol of zinc acetate [Zn(acet)₂], 10 mL of oleic acid, and 20 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

0.4 mmol of selenium powder and 4 mmol of sulfur powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 1.

0.1 mmol of selenium powder and 0.3 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 2.

0.8 mmol of selenium powder and 0.8 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 3.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 1 may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se_(y)S_(1-y). After 5 minutes of reaction, 2 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 2 may be added dropwise to the reaction system with an injection rate of 6 mL/h. Further, 3 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 3 and 6 mL of the cadmium oleate precursor may then be added dropwise to the reaction system with injection rates of 3 mL/h and 6 mL/h, respectively. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a green QD (CdZn₃SeS₃/Zn₄SeS₃/Cd₃Zn₅Se₄S₄) having a QW energy-level structure may be obtained.

Embodiment 20: Preparation of a Red QD with the Specific Structure 3

Preparation of a cadmium oleate and zinc oleate precursor: 0.8 mmol of cadmium oxide (CdO), 12 mmol of zinc acetate [Zn(acet)₂], 14 mL of oleic acid, and 20 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

0.2 mmol of selenium powder and 0.6 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

0.9 mmol of cadmium oxide (CdO), 0.9 mL of oleic acid, and 8.1 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se. After 10 minutes of reaction, 2 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 2 mL/h. After 30 minutes of injection, 3 mL of the cadmium oleate precursor may then be simultaneously added dropwise to the reaction system with an injection rate of 6 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a red QD (Cd_(x)Zn_(1-x)Se/ZnSe_(y)S_(1-y)/Cd_(z)Zn_(1-z)SeS) having a QW energy-level structure may be obtained.

Embodiment 21: Preparation of a Blue QD with the Specific Structure 4

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.2 mmol of selenium powder may be dissolved in 1 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)S. After 10 minutes of reaction, the cadmium oleate precursor and the sulfur-trioctylphosphine precursor may be continuously injected into the reaction system with injection rates of 0.6 mmol/h and 0.6 mmol/h, respectively for 20 minutes. Further, the cadmium oleate precursor and the sulfur-trioctylphosphine precursor may then be continuously injected into the reaction system with injection rates of 0.4 mmol/h and 0.6 mmol/h, respectively for 1 hour. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol and precipitated, and then purified by centrifugation. As such, a blue QD (CdZnS/CdZnSe/CdZnS) having a QW energy-level structure may be obtained.

Embodiment 22: Preparation of a Green QD with the Specific Structure 4

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.4 mmol of selenium powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

0.8 mmol of cadmium oxide (CdO), 1.2 mL of oleic acid, and 4.8 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)S. After 10 minutes of reaction, the cadmium oleate precursor and the selenium-trioctylphosphine may be injected continuously into the reaction system with injection rates of 0.6 mmol/h and 0.6 mmol/h, respectively for 40 minutes. Further, the cadmium oleate precursor and the sulfur-trioctylphosphine precursor may then be injected continuously into the reaction system with injection rates of 0.4 mmol/h and 6 mmol/h, respectively for 1 hour. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a green QD (CdZnS/CdZnSe/CdZnS) having a QW energy-level structure may be obtained.

Embodiment 23: Preparation of a Red QD with the Specific Structure 4

Preparation of a cadmium oleate and zinc oleate precursor: 0.8 mmol of cadmium oxide (CdO), 12 mmol of zinc acetate [Zn(acet)₂], 14 mL of oleic acid, and 20 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

1.5 mmol of selenium powder and 1.75 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 1.

1 mmol of selenium powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

0.2 mmol of selenium powder and 0.8 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 2.

3 mmol of cadmium oxide (CdO), 3 mL of oleic acid, and 6 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 1 may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se. After 10 minutes of reaction, 2 mL of the selenium-trioctylphosphine precursor and 3 mL of the cadmium oleate precursor may be added dropwise to the reaction system with injection rates of 4 mL/h and 6 mL/h, respectively. After 30 minutes of injection, 2 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor 2 and 3 mL of the cadmium oleate precursor may be added dropwise to the reaction system with injection rates of 2 mL/h and 3 mL/h, respectively. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a red QD (Cd_(x)Zn_(1-x)Se/CdZnSe/Cd_(z)Zn_(1-z)SeS) having a QW energy-level structure may be obtained.

Embodiment 24: Preparation of a Blue QD with the Specific Structure 5

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

1 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)S. After 10 minutes of reaction, 3 mL of the sulfur-trioctylphosphine precursor may be continuously injected into the reaction system with an injection rate of 3 mL/h. Then, 20 minutes after starting the injection of the sulfur-trioctylphosphine precursor, 2 mL of the cadmium oleate precursor may be continuously injected into the reaction system with an injection rate of 6 mL/h. Further, 40 minutes after starting the injection of the sulfur-trioctylphosphine precursor, 4 mL of the cadmium oleate precursor may be continuously injected into the reaction system with an injection rate of 12 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol and precipitated, and then purified by centrifugation. As such, a blue QD (CdZnS/ZnS/CdZnS) having a QW energy-level structure may be obtained.

Embodiment 25: Preparation of a Green QD with the Specific Structure 5

Preparation of a cadmium oleate and zinc oleate precursor: 0.4 mmol of cadmium oxide (CdO), 6 mmol of zinc acetate [Zn(acet)₂], 10 mL of oleic acid, and 20 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

0.4 mmol of selenium powder and 4 mmol of sulfur powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se_(y)S_(1-y). After 10 minutes of reaction, 3 mL of the sulfur-trioctylphosphine precursor may be injected continuously into the reaction system with an injection rate of 3 mL/h. Then, 20 minutes after starting the injection of the sulfur-trioctylphosphine precursor, 2 mL of the cadmium oleate precursor may be continuously injected into the reaction system with an injection rate of 6 mL/h. Further, 40 minutes after starting the injection of the sulfur-trioctylphosphine precursor, 4 mL of the cadmium oleate precursor may be continuously injected into the reaction system with an injection rate of 12 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a green QD (CdZnSeS/ZnS/CdZnS) having a QW energy-level structure may be obtained.

Embodiment 26: Preparation of a Red QD with the Specific Structure 5

Preparation of a cadmium oleate and zinc oleate precursor: 0.8 mmol of cadmium oxide (CdO), 12 mmol of zinc acetate [Zn(acet)₂], 14 mL of oleic acid, and 20 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se. After 10 minutes of reaction, the sulfur-trioctylphosphine precursor may be injected continuously into the reaction system with an injection rate of 6 mmol/h for 1 hour. Then, 20 minutes after starting the injection of the sulfur-trioctylphosphine precursor, 0.2 mmol of the cadmium oleate precursor may be continuously injected into the reaction system with an injection rate of 0.6 mmol/h. Further, 40 minutes after starting the injection of the sulfur-trioctylphosphine precursor, 4 mmol of the cadmium oleate precursor may be continuously injected into the reaction system with an injection rate of 1.2 mmol/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a red QD (CdZnSe/ZnS/CdZnS) having a QW energy-level structure may be obtained.

Embodiment 27: Preparation of a Blue QD with the Specific Structure 6

Preparation of a cadmium oleate and zinc oleate precursor: 1 mmol of cadmium oxide (CdO), 9 mmol of zinc acetate [Zn(acet)₂], 8 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain a transparent cadmium oleate precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)S. After 10 minutes of reaction, the sulfur-trioctylphosphine precursor and the cadmium oleate precursor may be added dropwise to the reaction system with injection rates of 6 mmol/h and 0.6 mmol/h, respectively. 30 minutes later, the temperature of the reaction system may be reduced to 280° C. Further, the remaining sulfur-trioctylphosphine precursor and the remaining cadmium oleate precursor may be added dropwise to the reaction system with injection rates of 6 mmol/h and 0.6 mmol/h, respectively. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol and precipitated, and then purified by centrifugation. As such, a blue QD (Cd_(x)Zn_(1-x)S) having the specific structure 6 may be obtained.

Embodiment 28: Preparation of a Green QD with the Specific Structure 6

Preparation of a cadmium oleate and zinc oleate precursor: 0.4 mmol of cadmium oxide (CdO), 8 mmol of zinc acetate [Zn(acet)₂], and 10 mL of oleic acid may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder and 4 mmol of sulfur powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

2 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be rapidly injected into the reaction system to form Cd_(x)Zn_(1-x)Se_(y)S_(1-y). After 10 minutes of reaction, the temperature of the reaction system may be reduced to 280° C. Further, the sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 4 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a green QD (Cd_(x)Zn_(1-x)Se_(y)S_(1-y)/ZnS) having the specific structure 6 may be obtained.

Embodiment 29: Preparation of a Red QD with the Specific Structure 6

Preparation of a cadmium oleate and zinc oleate precursor: 0.8 mmol of cadmium oxide (CdO), 12 mmol of zinc acetate [Zn(acet)₂], and 14 mL of oleic acid may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the cadmium oleate and zinc oleate precursor. Then, the cadmium oleate and zinc oleate precursor may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

2 mmol of selenium powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine precursor may be prepared.

0.2 mmol of selenium powder and 0.6 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine may be rapidly injected into the reaction system, and Cd_(x)Zn_(1-x)Se may quickly nucleate. After 10 minutes of reaction, the temperature of the reaction system may be reduced to 280° C. Further, the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 4 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a red QD (Cd_(x)Zn_(1-x)Se/ZnSeS) having the specific structure 6 may be obtained.

Embodiment 30: Preparation of a Blue QD with the Specific Structure 7

Preparation of a first cadmium oleate precursor: 1 mmol of cadmium oxide (CdO), 1 mL of oleic acid, and 5 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. Then, the first cadmium oleate precursor 1 may be stored in a nitrogen environment at the same temperature (i.e., 80° C.) for later use.

Preparation of a second cadmium oleate precursor: 0.6 mmol of cadmium oxide (CdO), 0.6 mL of oleic acid, and 5.4 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be heated under reflux in a nitrogen environment at 250° C. for 120 minutes to obtain the transparent second cadmium oleate precursor 2.

Preparation of a zinc oleate precursor: 9 mmol of zinc acetate [Zn(acet)₂], 7 mL of oleic acid, and 10 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. Then, the environment may be changed to a nitrogen environment, and after heated under reflux in the nitrogen environment at 250° C., the obtained zinc oleate precursor may be stored for later use.

2 mmol of sulfur powder may be dissolved in 3 mL of 1-octadecene to form a sulfur-1-octadecene precursor.

6 mmol of sulfur powder may be dissolved in 3 mL of trioctylphosphine to form a sulfur-trioctylphosphine precursor may be prepared.

Under a nitrogen environment, the cadmium oleate precursor 1 may be heated to 310° C., and then the sulfur-1-octadecene precursor may be rapidly injected into the reaction system to form CdS. After 10 minutes of reaction, the zinc oleate precursor may be completely injected into the reaction system, and then 3 mL of the sulfur-trioctylphosphine precursor and 6 mL of the cadmium oleate precursor 2 may be simultaneously injected into the reaction system with injection rates of 3 mL/h and 4 mL/h, respectively.

After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a blue QD having a QW energy-level structure may be obtained.

Embodiment 31: Preparation of a Green QD with the Specific Structure 7

Preparation of a cadmium oleate precursor: 0.4 mmol of cadmium oxide (CdO), 1 mL of oleic acid, and 5 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. The cadmium oleate precursor may then be obtained after being heated under reflux in a nitrogen environment at 250° C. Further, the cadmium oleate precursor may be stored in the nitrogen environment at the same temperature for later use.

0.4 mmol of selenium powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine.

Preparation of a zinc oleate precursor: 8 mmol of zinc acetate [Zn(acet)₂], 9 mL of oleic acid, and 15 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. Then, the environment may be changed to a nitrogen environment, and after heated under reflux in the nitrogen environment at 250° C. for 120 minutes, the obtained zinc oleate precursor may be stored for later use.

2 mmol of sulfur powder and 1.6 mmol of selenium powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine precursor may be rapidly injected into the reaction system to form CdSe. After 5 minutes of reaction, the zinc oleate precursor may be completely injected into the reaction system, and then 2 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 2 mL/h until the precursor is completely injected. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a green fluorescent QD having a QW energy-level structure may be obtained.

Embodiment 32: Preparation of a Red QD with the Specific Structure 7

Preparation of a cadmium oleate precursor: 0.8 mmol of cadmium oxide (CdO), 4 mL of oleic acid, and 10 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. The cadmium oleate precursor may then be obtained after being heated under reflux in a nitrogen environment at 250° C. Further, the cadmium oleate precursor may be stored at the same temperature for later use.

Preparation of a zinc oleate precursor: 12 mmol of zinc acetate [Zn(acet)₂], 10 mL of oleic acid, and 10 mL of 1-octadecene may be placed in a 100 mL three-neck flask, and may then be degassed for 60 minutes under vacuum at a temperature of 80° C. to obtain the zinc oleate precursor.

0.8 mmol of selenium powder may be dissolved in 4 mL of trioctylphosphine to form a selenium-trioctylphosphine.

1 mmol of selenium powder and 0.6 mmol of sulfur powder may be dissolved in 2 mL of trioctylphosphine to form a selenium-trioctylphosphine and sulfur-trioctylphosphine precursor.

Under a nitrogen environment, the cadmium oleate and zinc oleate precursor may be heated to 310° C., and then the selenium-trioctylphosphine precursor may be rapidly injected into the reaction system to quickly form CdSe. After 10 minutes of reaction, the zinc oleate precursor may be completely injected into the reaction system, and then 2 mL of the selenium-trioctylphosphine and sulfur-trioctylphosphine precursor may be added dropwise to the reaction system with an injection rate of 4 mL/h. After the reaction is completed and the reaction system is cooled down to room temperature, the reaction product may be repeatedly dissolved with toluene and anhydrous methanol, precipitated, and then purified by centrifugation. As such, a red fluorescent QD having a QW energy-level structure may be obtained.

Embodiment 33

As shown in FIG. 11 , an exemplary QD light-emitting diode may include, from the bottom to the top, an indium tin oxide (ITO) substrate 11, a bottom electrode 12, a PEDOT:PSS [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate] hole-injection layer 13, a poly-TPD [poly(4-butylphenyl-diphenyl-amine)] hole-transport layer 14, a light-emitting layer 15, a ZnO electron-transport layer 16, and an A1 top electrode 17.

The QD light-emitting diode may be prepared by an exemplary method including the following steps.

After a bottom electrode 12, a PEDOT:PSS hole-injection layer 13 with a thickness of 30 nm, and a poly-TPD hole-transport layer 14 with a thickness of 30 nm are sequentially prepared on an ITO substrate 11, a QD light-emitting layer 15 with a thickness of 20 nm may be prepared on the poly-TPD hole-transport layer 14. Further, a ZnO electron-transport layer 16 with a thickness of 40 nm, and an A1 top electrode 17 with a thickness of 100 nm may be formed on the QD light-emitting layer 15. The QD composite material of the QD light-emitting layer 15 may be a QD composite material in Embodiment 10 of the present invention.

Embodiment 34

As shown in FIG. 12 , an exemplary QD light-emitting diode may include, from the bottom to the top, an ITO substrate 21, a bottom electrode 22, a PEDOT:PSS hole-injection layer 23, a PVK [poly(9-vinylcarbazole)] hole-transport layer 24, a light-emitting layer 25, a ZnO electron-transport layer 26, and an A1 top electrode 27.

The QD light-emitting diode may be prepared by an exemplary method including the following steps.

After a bottom electrode 22, a PEDOT:PSS hole-injection layer 23 with a thickness of 30 nm, and a PVK hole-transport layer 24 with a thickness of 30 nm are sequentially prepared on an ITO substrate 21, a QD light-emitting layer 25 with a thickness of 20 nm may be prepared on the PVK hole-transport layer 24. Further, a ZnO electron-transport layer 26 with a thickness of 40 nm, and an A1 top electrode 27 with a thickness of 100 nm may be formed on the QD light-emitting layer 25. The QD composite material of the QD light-emitting layer 25 may be a QD composite material in Embodiment 15 of the present invention.

Embodiment 35

As shown in FIG. 13 , an exemplary QD light-emitting diode may include, from the bottom to the top, an ITO substrate 31, a bottom electrode 32, a PEDOT:PSS hole-injection layer 33, a poly-TPD hole-transport layer 34, a light-emitting layer 35, a TPBi [2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)] electron-transport layer 36, and an A1 top electrode 37.

The QD light-emitting diode may be prepared by an exemplary method including the following steps.

After a bottom electrode 32, a PEDOT:PSS hole-injection layer 33 with a thickness of 30 nm, and a poly-TPD hole-transport layer 34 with a thickness of 30 nm are sequentially prepared on an ITO substrate 31, a QD light-emitting layer 35 with a thickness of 20 nm may be prepared on the poly-TPD hole-transport layer 34. Further, a TPBi electron-transport layer 36 with a thickness of 40 nm, and an A1 top electrode 37 with a thickness of 100 nm may be formed on the QD light-emitting layer 35 through evaporation under vacuum. The QD composite material of the QD light-emitting layer 35 may be a QD composite material in Embodiment 18 of the present invention.

Embodiment 36

As shown in FIG. 14 , an exemplary QD light-emitting diode may include, from the bottom to the top, an ITO substrate 41, a bottom electrode 42, a ZnO electron-transport layer 43, a light-emitting layer 44, a NPB [N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine]hole-transport layer 45, a MoO₃ hole-injection layer 46, and an A1 top electrode 47.

The QD light-emitting diode may be prepared by an exemplary method including the following steps.

A bottom electrode 42 and a ZnO electron-transport layer 43 with a thickness of 40 nm may be sequentially prepared on an ITO substrate 41. A light-emitting layer 44 with a thickness of 20 nm may be formed on the ZnO electron-transport layer 43. Further, a NPB hole-injection layer 45 with a thickness of 30 nm, a MoO₃ hole-injection layer 46 with a thickness of 5 nm, and an A1 top electrode 47 with a thickness of 100 nm may then be prepared through evaporation under vacuum. The QD composite material of the QD light-emitting layer 44 may be a QD composite material in Embodiment 21 of the present invention.

Embodiment 37

As shown in FIG. 15 , an exemplary QD light-emitting diode may include, from the bottom to the top, a glass substrate 51, an A1 electrode 52, a PEDOT:PSS hole-injection layer 53, a poly-TPD hole-transport layer 54, a light-emitting layer 55, a ZnO electron-transport layer 56, and an ITO top electrode 57.

The QD light-emitting diode may be prepared by an exemplary method including the following steps.

An A1 electrode 52 with a thickness of 100 nm may be formed on a glass substrate 51 through evaporation under vacuum. Further, after a PEDOT:PSS hole-injection layer 53 with a thickness of 30 nm, and a poly-TPD hole-transport layer 54 with a thickness of 30 nm are sequentially prepared, a QD light-emitting layer 55 with a thickness of 20 nm may be prepared on the poly-TPD hole-transport layer 54. Then, a ZnO electron-transport layer 56 with a thickness of 40 nm may be prepared on the QD light-emitting layer 55. Moreover, through a sputtering method, an ITO layer with a thickness of 120 nm may be formed as a top electrode 57. The QD composite material of the QD light-emitting layer 55 may be a QD composite material in Embodiment 24 of the present invention.

Embodiment 38

As shown in FIG. 16 , an exemplary QD light-emitting diode may include, from the bottom to the top, a glass substrate 61, an A1 electrode 62, a ZnO electron-transport layer 63, a light-emitting layer 64, a NPB hole-transport layer 65, a MoO₃ hole-injection layer 66, and an ITO top electrode 67.

The QD light-emitting diode may be prepared by an exemplary method including the following steps.

An A1 electrode 62 with a thickness of 100 nm may be formed on a glass substrate 61 through evaporation under vacuum. Then, a ZnO electron-transport layer 63 with a thickness of 40 nm, a QD light-emitting layer 64 with a thickness of 20 nm may be sequentially prepared. Further, a NPB hole-injection layer 65 with a thickness of 30 nm and a MoO₃ hole-injection layer 66 with a thickness of 5 nm may then be prepared through evaporation under vacuum. Moreover, through a sputtering method, an ITO layer with a thickness of 120 nm may be formed as a top electrode 67. The QD composite material of the QD light-emitting layer 64 may be a QD composite material in Embodiment 27 of the present invention.

It should be understood that the application of the present invention is not limited to the above examples and can be improved or transformed by those skilled in the art based on the above description. All these improvements and transformations should fall within the protection scope of the appended claims of the present invention. 

What is claimed is:
 1. A method for preparing a quantum dot (QD) composite material, comprising: synthesizing a first compound; synthesizing a second compound on a surface of the first compound, wherein the second compound and the first compound have different alloy compositions; and forming the QD composite material through a cation exchange reaction between the first compound and the second compound, wherein a light-emission peak wavelength of the QD composite material experiences an unchanged part and then blue-shift, wherein: the QD composite material includes at least two QD structural units arranged sequentially along a radial direction; the at least two structural units include a type A1 structural unit and a type A2 structural unit, wherein the type A1 QD structural unit has a gradient alloy composition structure with an energy level width increasing along the radial direction toward a surface, and the type A2 QD structural unit has a gradient alloy composition structure with the energy level width decreasing along the radial direction toward the surface; and the two types of QD structural units are arranged alternately along the radial direction, the energy levels in adjacent QD structural units having gradient alloy composition structures am continuous, and wherein: the cation exchange reaction between the first compound and the second compound is performed under a heating condition; a heating temperature is in a range of approximately 100° C. to 400° C.; and a heating time is in a range of approximately 2 seconds to 24 hours.
 2. The method for preparing the QD composite material according to claim 1, wherein: a cation precursor of the first compound and/or the second compound includes a zinc precursor, wherein the zinc precursor includes at least one of dimethyl zinc, diethyl zinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide, zinc peroxide, zinc perchlorate, zinc sulfate, zinc oleate, and zinc stearate.
 3. The method for preparing the QD composite material according to claim 1, wherein: a cation precursor of the first compound and/or the second compound includes a cadmium precursor, wherein the cadmium precursor includes at least one of dimethyl cadmium, diethyl cadmium, cadmium acetate, cadmium acetylacetonate, cadmium iodide, cadmium bromide, cadmium chloride, cadmium fluoride, cadmium carbonate, cadmium phosphate, cadmium nitrate, cadmium oxide, cadmium peroxide, cadmium perchlorate, cadmium sulfate, cadmium oleate, and cadmium stearate.
 4. The method for preparing the QD composite material according to claim 1, wherein: an anion precursor of the first compound and/or the second compound includes a selenium precursor, wherein the selenium precursor includes at least one of Se-TOP (selenium-trioctylphosphine), Se-TBP (selenium-tributylphosphine), Se-TPP (selenium-triphenylphosphine), Se-ODE (selenium-1-octadecene), Se-OA (selenium-oleic acid), Se-ODA (selenium-octadecylamine), Se-TOA (selenium-trioctylamine), Se-ODPA (selenium-octadecylphosphonic acid), and Se-OLA (selenium-oleylamine).
 5. The method for preparing the QD composite material according to claim 1, wherein: an anion precursor of the first compound and/or the second compound includes a sulfur precursor, wherein the sulfur precursor includes at least one of S-TOP (sulfur-trioctylphosphine), S-TBP (sulfur-tributylphosphine), S-TPP (sulfur-triphenylphosphine), S-ODE (sulfur-1-octadecene), S-OA (sulfur-oleic acid), S-ODA (sulfur-octadecylamine), S-TOA (sulfur-trioctylamine), S-ODPA (sulfur-octadecylphosphonic acid), S-OLA (sulfur-oleylamine), and alkyl thiol.
 6. The method for preparing the QD composite material according to claim 1, wherein: a molar feed ratio of a cationic precursor to an anion precursor used for forming the first compound is in a range of approximately 100:1 to 1:50.
 7. The method for preparing the QD composite material according to claim 1, wherein: a molar feed ratio of a cationic precursor to an anion precursor used for forming the second compound is in a range of approximately 100:1 to 1:50.
 8. The method according to claim 1, wherein the QD structural unit includes a gradient alloy composition structure or a homogenous alloy composition structure having Group II elements and Group VI elements.
 9. The method according to claim 1, wherein each of the QD structural units includes 2-20 monatomic layers, or each of the QD structural units includes 1-10 unit-cell layers.
 10. The method according to claim 9, wherein: the unit-cell layer is a smallest structural unit; within each unit-cell layer, lattice parameters and elements are the same; each QD structural unit is a closed unit-cell surface formed through a connection of the unit-cell layers; and an energy level width has a continuous change between adjacent unit-cell layers.
 11. The method according to claim 1, wherein a light-emission peak wavelength is in a range of 400 nm to 700 nm.
 12. The method according to claim 1, wherein a full width at half maximum of the light-emission peak of the QD composite material is in a range of 12 nm to 80 nm.
 13. The method according to claim 1, wherein each of the QD structural units has an alloy composition of Cd_(x1)Zn_(1-x1)Se_(y1)S_(1-y1), 0≤x1≤1, 0≤y1≤1, x1 and y1 being not both 0 or 1 at the same time.
 14. The method according to claim 13, wherein: a QD structural unit of the QD composite material has a gradient alloy composition structure with an energy level width increasing along the radial direction from a center to a surface, the alloy composition is Cd_(x0)Zn_(1-x0)Se_(y0)S_(1-y0), the alloy composition at point A is Cd_(x0) ^(A)Zn_(1-x0) ^(A)Se_(y0) ^(A)S_(1-y0) ^(A); and the alloy composition at point B is Cd_(x0) ^(B)Zn_(1-x0) ^(B)Se_(y0) ^(B)S_(1-y0) ^(B) point A being closer to a center of the QD composite material than point B, and the compositions at point A and point B satisfying: _(x0) ^(A)>_(x0) ^(B), _(y0) ^(A)>_(y0) ^(B).
 15. The method according to claim 13, wherein: a QD structural unit of the QD composite material has a gradient alloy composition structure with an energy level width decreasing along the radial direction from a center to a surface, the alloy composition is Cd_(x0)Zn_(1-x0)Se_(y0)S_(1-y0), the alloy composition at point C being Cd_(x0) ^(C)Zn_(1-x0) ^(C)Se_(y0) ^(C)S_(1-y0) ^(C), the alloy composition at point D being Cd_(x0) ^(D)Zn_(1-x0) ^(D)Se_(y0) ^(D)S_(1-y0) ^(D), point C being closer to a center of the QD composite material than point D, and the compositions at point E and point F satisfying: _(x0) ^(C)<_(x0) ^(D), _(y0) ^(C)<_(y0) ^(D). 